Sps receiver with adjustable linearity

ABSTRACT

A method of selecting a mode for an SPS receiver includes selecting either a first mode or a second mode for the SPS receiver based on a comparison between an output power of a communications transceiver and a mode switch point wherein the mode switch point is a power value. The first mode corresponds to a first bias current value of the SPS receiver, the second mode corresponds to a second bias current value of the SPS receiver, and the first bias current value is different from the second bias current value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of, and claims priorityto, U.S. patent application Ser. No. 11/753,542, entitled “SPS RECEIVERWITH ADJUSTABLE LINEARITY,” filed May 24, 2007, which claims the benefitof U.S. Provisional Application No. 60/891,873, entitled “A DYNAMICLINEARITY ADJUSTABLE GPS RF FRONT-END CIRCUIT BASED ON INTEGRATEDTRANSMITTER POWER,” filed Feb. 27, 2007, all of which are assigned tothe assignee hereof, and expressly incorporated herein by reference.

BACKGROUND

I. Field

The present disclosure relates generally to electronics circuits, andmore specifically to a receiver.

II. Background

A receiver is an electronics unit that receives and conditions a radiofrequency (RF) input signal. A receiver may perform various types ofsignal conditioning such as low noise amplification, filtering,frequency downconversion, etc.

The design of a receiver is challenging due to various designconsiderations such as performance, power consumption, etc. For manyapplications, high performance is required in order to meet systemspecifications and/or to achieve good overall performance. Theperformance of a receiver may be characterized by various parameterssuch as linearity, dynamic range, and noise performance. Linearityrefers to the ability to amplify a signal without generating a largeamount of distortion. Dynamic range refers to the range of receivedsignal levels that the receiver is expected to handle. Noise performancerefers to the amount of noise generated by the receiver. For certainapplications, low power consumption is also highly desirable. Forexample, a receiver may be used in a portable device such as a cellularphone, and low power consumption may extend battery life betweenrecharges, which is highly desirable.

There is therefore a need in the art for a receiver that can providegood performance with low power consumption.

SUMMARY

A receiver that can provide good performance with low power consumptionis described herein. The receiver may be a satellite positioning system(SPS) receiver used to condition signals received from satellites. TheSPS receiver may be co-located with a transmitter, which may betransmitting at the same time that the SPS receiver is operating. Largeoutput power from the transmitter may degrade the performance of the SPSreceiver.

The SPS receiver may be operated in one of a plurality of modes, whichmay be associated with different bias current settings for the SPSreceiver. One of the modes may be selected based on an output powerlevel of the transmitter. The SPS receiver may include at least onecircuit block with adjustable bias current, e.g., a low noise amplifier(LNA), a mixer, a local oscillator (LO) generator, etc. The bias currentof each circuit block may be set in accordance with the selected mode.

In one design, a first mode (e.g., a lower power mode) may be selectedfor the SPS receiver if the transmitter output power level is below aswitch point. A second mode (e.g., a high linearity mode) may beselected for the SPS receiver if the transmitter output power level isabove the switch point. The second mode is associated with more biascurrent for the SPS receiver than the first mode. Hysteresis may be usedfor the transitions between the first and second modes.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless device transmitting and receiving signals.

FIG. 2 shows a block diagram of the wireless device.

FIG. 3 shows probability density functions of transmitter output power.

FIG. 4 shows a state diagram for an SPS receiver within the wirelessdevice.

FIG. 5 shows a schematic diagram of an interrupt generation circuit.

FIG. 6 shows a schematic diagram of an LNA within the SPS receiver.

FIG. 7 shows a schematic diagram of a mixer within the SPS receiver.

FIG. 8 shows a schematic diagram of an LO generator for the SPSreceiver.

FIG. 9 shows a process for operating the SPS receiver.

FIG. 10 shows a process for selecting a mode for the SPS receiver.

DETAILED DESCRIPTION

FIG. 1 shows a wireless device 110 capable of communicating with awireless communication system 100. Wireless device 110 may also bereferred to as a mobile station, a user equipment (UE), a terminal, anaccess terminal, a subscriber unit, a station, etc. Wireless device 110may be a cellular phone, a personal digital assistant (PDA), a handhelddevice, a wireless modem, a laptop computer, a cordless phone, etc.Wireless device 110 may communicate with one or more base stations 120in system 100 at any given moment. A base station is a fixed station andmay also be referred to as a Node B, an access point, etc.

In general, wireless device 110 may be able to communicate with anynumber of wireless communication systems and networks. The terms“networks” and “systems” are often used interchangeably. For example,wireless device 110 may be able to communicate with a Code DivisionMultiple Access (CDMA) system, a Time Division Multiple Access (TDMA)system, a Frequency Division Multiple Access (FDMA) system, anOrthogonal FDMA (OFDMA) system, a Single-Carrier FDMA (SC-FDMA) system,etc. A CDMA system may implement a radio technology such as UniversalTerrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband-CDMA (W-CDMA) and Low Chip Rate (LCR). cdma2000 covers IS-2000,IS-95 and IS-856 standards. IS-2000 Releases 0 and A are commonlyreferred to as CDMA2000 1×, or simply, 1×. A TDMA system may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA system may implement a radio technology such as Evolved UTRA(E-UTRA), IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, andGSM are described in documents from an organization named “3rdGeneration Partnership Project” (3GPP). cdma2000 is described indocuments from an organization named “3rd Generation Partnership Project2” (3GPP2). These various radio technologies and standards are known inthe art. Wireless device 110 may also be able to communicate with awireless local area network (WLAN), a wireless personal area network(WPAN), etc.

Wireless device 110 is also capable of receiving signals from satellites130. Satellites 130 may belong to a satellite positioning system (SPS)such as the United States Global Positioning System (GPS), the EuropeanGalileo system, the Russian Glonass system, etc. GPS is a constellationof 24 well-spaced satellites that orbit the earth. Each GPS satellitetransmits a GPS signal encoded with information that allows GPSreceivers on earth to measure the time of arrival of the received GPSsignal relative to an arbitrary point in time. This relativetime-of-arrival measurement may be converted to a pseudo-range. Theposition of wireless device 110 may be accurately estimated based onpseudo-range measurements for a sufficient number of satellites andtheir known locations.

FIG. 2 shows a block diagram of a design of wireless device 110. In thisdesign, wireless device 110 includes a transceiver 218 with onetransmitter 220 and two receivers 240 and 260. Transmitter 220 andreceiver 240 may be used for communication with system 100. Receiver 260may be used to receive signals from satellites 130 and may also bereferred to as an SPS receiver. In general, wireless device 110 mayinclude any number of transmitters and any number of receivers for anynumber of communication systems and frequency bands. In the design shownin FIG. 2, transmitter 220 and receiver 240 are coupled to an antenna238, and receiver 260 is coupled to another antenna 258. In general, thetransmitters and receivers may be coupled to any number of antennas,e.g., transmitter 220 and receivers 240 and 260 may be coupled to asingle antenna.

A transmitter or a receiver may be implemented with a super-heterodynearchitecture or a direct-conversion architecture. In thesuper-heterodyne architecture, a signal is frequency converted betweenRF and baseband in multiple stages, e.g., from RF to an intermediatefrequency (IF) in one stage, and then from IF to baseband in anotherstage for a receiver. In the direct-conversion architecture, which isalso referred to as zero-IF architecture, a signal is frequencyconverted between RF and baseband in one stage. The super-heterodyne anddirect-conversion architectures may use different circuit blocks and/orhave different requirements. In the design shown in FIG. 2, transmitter220 and receiver 240 are implemented with the direct-conversionarchitecture, and receiver 260 is implemented with the super-heterodynearchitecture.

For data transmission, a data processor 210 processes data to betransmitted and provides an analog output signal to transmitter 220 intransceiver 218. Within transmitter 220, the analog output signal isamplified by an amplifier (Amp) 222, filtered by a lowpass filter 224 toremove images caused by digital-to-analog conversion, amplified by avariable gain amplifier (VGA) 226, and upconverted from baseband to RFby a mixer 228. The upconverted signal is filtered by a bandpass filter230 to remove images caused by the frequency upconversion, furtheramplified by a power amplifier (PA) 232, routed through a duplexer 234,and transmitted from antenna 238.

For data reception, antenna 238 receives downlink signals from basestations and provides a first received RF signal, which is routedthrough duplexer 234 and provided to receiver 240. Within receiver 240,the first received RF signal is filtered by a bandpass filter 242,amplified by an LNA 244, and downconverted from RF to baseband by amixer 246. The downconverted signal is amplified by a VGA 248, filteredby a lowpass filter 250, and amplified by an amplifier 252 to obtain afirst analog input signal, which is provided to data processor 210.

For SPS, antenna 258 receives SPS signals from satellites 130 andprovides a second received RF signal to SPS receiver 260. Within SPSreceiver 260, the second received RF signal is filtered by a bandpassfilter 262, amplified by an LNA 264, and downconverted from RF to IF bya mixer 266. The IF signal is amplified by an amplifier 268 anddownconverted from IF to baseband by a mixer 270. The downconvertedsignal is amplified by an amplifier 272, filtered by a lowpass filter274, and buffered by a driver 276 to obtain a second analog inputsignal, which is provided to data processor 210. Although not shown inFIG. 2, an IF filter may be placed between mixers 266 and 270 and usedto filter the downconverted signal.

A phase locked loop (PLL) 282 generates carrier signals at desiredfrequencies. LO generators 284 receive one or more carrier signals fromPLL 282 and generate LO signals used for frequency upconversion by mixer228 and frequency downconversion by mixers 246 and 270. An LO generator286 receives a carrier signal from PLL 282 and generates an LO signalused for frequency downconversion by mixer 266. A bias control unit 278receives information for transmitter 220 and/or SPS receiver 260 andgenerates bias controls for circuit blocks such as LNA 264, mixer 266,amplifier 268, LO generator 286, etc. Unit 278 may provide bias currentsto these circuit blocks or may provide control signals used to set thebias currents of these circuit blocks. Unit 278 may comprise register,logic, and/or other circuitry.

Data processor 210 may include various processing units for datatransmission and reception via system 100 and also for SPS processing.For example, data processor 210 may include a digital VGA (DVGA) 212that provides a selectable gain for data being sent via transmitter 220.Data processor 210 may include a digital signal processor (DSP) 213 thatperforms various functions for data transmission and reception and otheroperations. Data processor 210 may also include an SPS processor 214that performs processing for received SPS signals and an SPS receiver(RX) mode controller 216 that selects an operating mode for SPS receiver260. Data processor 210 may be an application specific integratedcircuit (ASIC) such as a mobile station modem (MSM). Acontroller/processor 290 may direct the operations of various processingunits in wireless device 110. A memory 292 may store data and programcodes for wireless device 110.

FIG. 2 shows an example transceiver design. In general, the conditioningof the signals in the transmitter and receivers may be performed by oneor more stages of amplifier, filter, mixer, etc. These circuit blocksmay be arranged differently from the configuration shown in FIG. 2.Furthermore, other circuit blocks not shown in FIG. 2 may also be usedto condition the signals in the transmitter and receivers.

FIG. 2 also shows an example SPS receiver design. In general, an SPSreceiver may implement the super-heterodyne architecture (as shown inFIG. 2) or the direct-conversion architecture (not shown in FIG. 2). TheSPS receiver design in FIG. 2 may provide certain advantages such as (1)simply LO generator for mixer 270 and (2) separate PLLs for transmitter220, receiver 240, and SPS receiver 260. For example, the LO generatorfor mixer 270 may be implemented with a divider that divides a referenceclock from a reference oscillator (e.g., a TCXO) by an integer ratio.

SPS receiver 260 may operate at the same time that transmitter 220 isactive. For example, transmitter 220 may be used for W-CDMA or cdma2000and may be active for an entire call. Transmitter 220 may also be usedfor GSM and may be active during the same time that SPS receiver 260 isactive. In any case, when transmitter 220 and SPS receiver 260 aresimultaneously active, large output power from transmitter 220 maydegrade the performance of SPS receiver 260. For example, a CDMA signalfrom transmitter 220 on an Advanced Wireless Services (AWS) band and anexternal CDMA or GSM signal on a Personal Communications Service (PCS)band may create large third-order inter-modulation distortion (IM3),which may fall within an SPS band and may be hard to distinguish fromthe received SPS signals. The magnitude of the IM3 may be dependent onthe linearity of SPS receiver 260. Hence, linearity requirements of SPSreceiver 260 may be more stringent due to high output power fromtransmitter 220. Large transmitter power leaking to the SPS receiverinput may also cause other nonlinearity such as second-orderinter-modulation (IM2) and gain compression, which may significantlydegrade the performance of the SPS receiver.

Various circuit blocks in SPS receiver 260 (e.g., LNA 264, mixer 266,and amplifier 268) may be biased with large amounts of current in orderto meet the worst-case linearity requirements imposed by the maximumoutput power from transmitter 220 and/or to reduce noise from LOgenerator 286. More bias current may be used to (i) prevent gaincompression from increasing the noise figure of SPS receiver 260, (ii)lower the noise floor of LO generator 286, since the jammer mayreciprocally mix the LO noise into the SPS band, and (iii) improvelinearity in order to reduce IM2 and IM3 that may fall in-band.Operating SPS receiver 260 with large amounts of bias current may ensuregood performance even with high transmitter output power. However,operating SPS receiver 260 with large amounts of bias current all thetime may result in excessive battery consumption since the transmitteroutput power may be much less than the maximum power most of the time.

FIG. 3 shows three probability density functions (PDFs) of output powerof a CDMA signal from transmitter 220 for three network test scenarios.The horizontal axis represents transmitter output power level, which isgiven in units of dBm. For 1×, the maximum output power is +24 dBm. Thevertical axis represents the probability of each transmitter outputpower level occurring. As shown in FIG. 3, the probability oftransmitting at maximum or high output power may be relatively small.

In an aspect, SPS receiver 260 may be biased with different amounts ofcurrent for different transmitter output power levels in order toachieve the desired linearity with low power consumption. In general,any number of modes may be supported for SPS receiver 260. Each mode maybe associated with (i) a different bias current setting for the circuitblocks within SPS receiver 260 and (ii) a range of transmitter outputpower levels within which the mode will be selected. In one design thatis described in detail below, two mode are supported—a high linearity(HL) mode and a low power (LP) mode. The HL mode utilizes more biascurrent to achieve better linearity for SPS receiver 260 and may beselected when the transmitter output power is high. The LP mode utilizesless bias current in order to reduce power consumption by SPS receiver260 and may be selected when the transmitter output power is not high.

A switch point or threshold may be used to select either the HL or LPmode for SPS receiver 260. The switch point may affect both thelikelihood of selecting the LP mode and the amount of bias current touse for the LP mode. The switch point may be defined to be (i) highenough so that SPS receiver 260 operates in the LP mode as often aspossible but (ii) low enough so that the amount of bias current used inthe LP mode is sufficiently low. The switch point may be defined to be+3 dBm (as shown in FIG. 3), +5 dbm, +10 dbm, +15 dbm, etc. The switchpoint may be static and used for all deployments and all frequencybands. Alternatively, the switch point may be dynamically varied fordifferent network deployments, different frequency bands, differentenvironments observed by wireless device 110, etc. For example, a PDFmay be generated for the environment observed by wireless device 110 andmay be used to select a suitable switch point. The bias currents of thecircuit blocks within SPS receiver 260 may be set based on the switchpoint.

A state machine may receive information regarding the current status ofSPS receiver 260 (e.g., on or off), the current status of transmitter220, and the current transmitter output power level. The transmitteroutput power level may be determined based on (i) a control unit thatsets the gain of transmitter 220 and which may be implemented byprocessor 210 or 290 in FIG. 2, (ii) a power detector that measures thetransmitter output power (not shown in FIG. 2), and/or (iii) some otherunit. For example, the transmitter output power level may be determinedbased on the gains of DVGA 212 and VGA 226 and the gain/range/state ofPA 232.

The state machine may receive information on transmitter output powerlevel in various manners. In one design, the state machine receives aninterrupt whenever the transmitter output power level crosses the switchpoint and updates its state accordingly. The interrupt may be generated,e.g., by DSP 213 within processor 210, by processor 290, etc. In anotherdesign, the state machine receives the current transmitter output powerlevel (e.g., by periodically polling DSP 213), determines whether thetransmitter output power level has crossed the switch point, and updatesits state accordingly.

In general, it may be desirable to know quickly when the transmitteroutput power level has exceeded the switch point, so that the HL modecan be selected quickly to mitigate degradation due to high transmitteroutput power. The transition from the HL mode to the LP mode may not betime sensitive and may be achieved, e.g., by periodically polling thetransmitter output power.

FIG. 4 shows a diagram of a design of a state machine 400 for SPSreceiver 260. In the design shown in FIG. 4, state machine 400 includesfour states 410, 411, 412 and 413, which are also denoted as states 0,1, 2 and 3, respectively. States 0, 1, 2 and 3are defined as follows:

-   -   State 0—SPS receiver 260 is off,    -   State 1—transmitter 220 is off, and SPS receiver 260 is in the        LP mode,    -   State 2—transmitter 220 is on, and SPS receiver 260 is in the LP        mode, and    -   State 3—transmitter 220 is on, and SPS receiver 260 is in the HL        mode.

State machine 400 may start in state 0 and, when SPS receiver 260 ispowered up, transition to either state 1 if transmitter 220 is off orstate 2 if transmitter 220 is on. State machine 400 may transition fromstate 1 to state 2 when transmitter 220 is powered up. State machine 400may transition from state 2 to state 3 upon receiving an interrupt dueto the transmitter output power level exceeding the switch point and maytransition from state 3 back to state 2 when the transmitter outputpower level falls below the switch point. State machine 400 maytransition from either state 2 or 3 back to state 1 when transmitter 220is powered down, and may transmission from state 1, 2 or 3 back to state0 when SPS receiver 260 is powered down.

FIG. 4 shows one design of a state machine for SPS receiver 260. Ingeneral, a state machine with any number of states and any trigger fortransitions between states may be used for SPS receiver 260.

In the design shown in FIG. 4, LNA 264 and mixer 266 (LNA/Mixer) may beswitched between the HL and LP modes, and LO generator 286 (LO Gen) mayalso be switched between the HL and LP modes. In general, any circuitblock within SPS receiver 260 may be switched between the HL and LPmodes. A given circuit block may also operate in the LP mode all thetime regardless of the transmitter output power.

Whether a given circuit block is switched between the HL and LP modesmay be dependent on the frequency band of transmitter 220 and/or otherfactors. The switch point may also be dependent on the frequency band. Alook-up table may store, for each frequency band, the switch point forthat frequency band and a list of circuit blocks in SPS receiver 260that should be switched between the HL and LP modes for that frequencyband.

Initialization may be performed when transitioning from either state 0or 1 to state 2. For the initialization, the frequency band fortransmitter 220 may be determined, the switch point to use for thefrequency band may be ascertained, and the list of circuit blocks toswitch between the HL and LP modes may be identified and provided tobias control unit 278. The generation of interrupt may be enabled sothat an interrupt is generated whenever the transmitter output powerexceeds the switch point.

SPS receiver 260 may be switched from the LP mode to the HL mode whentransitioning from state 2 to state 3 due to reception of an interruptindicating high transmitter output power. For the LP-to-HL transition,the interrupt generation may be disabled, SPS processor 214 may beblanked or disabled, SPS receiver 260 may be blanked or disabled (e.g.,by turning off LNA 264 and/or other circuit blocks) and then switched tothe HL mode, and a timer may be started. Upon expiration of the timer,SPS processor 214 and SPS receiver 260 may be resumed. Blanking refersto shutting off a circuit block or a processing unit. Blanking may beperformed in order to prevent strong interference from possiblycorrupting current SPS processing, e.g., SPS signal integration. Theinterference may be due to PLL 284 becoming unlocked when switching tothe HL mode. The timer duration may be selected to be sufficiently longto allow PLL 284 to relock. Blanking may be skipped if not needed, sothat processing gain is not degraded due to loss of SPS signal resultingfrom blanking.

While in the HL mode, the transmitter output power may be examinedperiodically to determine whether a transition back to the LP mode canbe made. In one design, time hysteresis is used to avoid continuallytoggling between the HL and LP modes. For this design, a transition fromthe HL mode to the LP mode may occur if the transmitter output power isbelow the switch point for L consecutive intervals or polling instances.L may be set to 3 or some other value. Time hysteresis may also beachieved in other manners. In another design, signal hysteresis is usedto avoid continually toggling between the HL and LP modes. For thisdesign, a transition from the LP mode to the HL mode may occur if thetransmitter output power level exceeds a high switch point, and atransition from the HL mode back to the LP mode may occur if thetransmitter output power level falls below a low switch point. Thedifference between the high and low switch points is the amount ofhysteresis. A combination of time and signal hysteresis may also be usedto avoid continually toggling between the HL and LP modes.

For an HL-to-LP transition, SPS processor 214 may be blanked, SPSreceiver 260 may be blanked and then switched to the LP mode, and atimer may be started. Upon expiration of the timer, SPS processor 214and SPS receiver 260 may be resumed, and the interrupt generation may beenabled to allow for fast transition to the HL mode if necessary. Thesteps for the HL-to-LP transition (except for the enabling of theinterrupt generation) may also be performed whenever transmitter 220 ispowered down while SPS receiver 260 is in the HL mode.

A change in frequency band for transmitter 220 may occur while SPSreceiver 260 is active. In this case, transmitter 220 may be temporarilydisabled for the band change, which may then result in a transition tostate 1 in FIG. 4. The initialization described above may be performedwhen transmitter 220 is enabled on the new frequency band. The switchpoint and the HL/LP circuit configuration may be updated for the newfrequency band by the initialization.

Transmitter 220 may be enabled but may actively transmit for only aportion of the time. For example, IS-95 supports puncturing of some bitswhen sending data at a rate that is lower than the maximum rate.Transmitter 220 may be blanked (e.g., applied with zero signal value)for the punctured bits. In W-CDMA, wireless device 110 may operate in acompressed mode in which transmitter 220 does not transmit during knowntransmission gaps in order for receiver 240 to make measurements. InGSM, transmitter 220 may be active in some time slots, and receiver 240may be active in some other time slots in a TDM manner. In any case,when transmitter 220 is not continuously transmitting, the transmitteroutput power may be determined as if transmitter 220 is continuouslyactive. This may be achieved by examining the transmitter output powerwhen transmitter 220 is actively transmitting and ignoring timeintervals when transmitter 220 is not actively transmitting. This mayavoid switching SPS receiver 260 to the LP mode simply because thetransmitter output power is examined at time instants in whichtransmitter 220 is momentarily not active.

The transmitter output power may be determined based on a transmittergain control word (TX_Gain) and a range for PA 232 (PA_R). The TX_Gainmay comprise the gains of all variable gain circuit blocks intransmitter 220, e.g., the gains of DVGA 212 and VGA 226. PA 232 mayoperate in one of multiple PA ranges. Each PA range may be associatedwith a specific gain for PA 232 and may be used for a specific range oftransmitter output power levels. The mapping between transmitter outputpower level and the combination of TX_Gain and PA_R may be determinedduring calibration and stored in a look-up table. The mapping may bedependent on frequency band, channel, temperature, etc. One mapping maybe stored in the look-up table for each operating scenario of interest,e.g., for each frequency band supported by transmitter 220.

FIG. 5 shows a schematic diagram of an interrupt generation circuit 500,which may be implemented within data processor 210 or bias control unit278 in FIG. 2. Circuit 500 may be used to generate an interrupt wheneverthe transmitter output power level exceeds the switch point, which maytrigger a transition from the LP mode to the HL mode. Circuit 500 mayalso be used to generate an interrupt whenever the transmitter outputpower level falls below the switch point, which may trigger a transitionfrom the HL mode to the LP mode.

In the design shown in FIG. 5, PA 232 operates in one of four PA ranges.A multiplexer (Mux) 512 receives four thresholds TH1, TH2, TH3 and TH4for the four PA ranges and provides the threshold corresponding to thecurrent PA range, as indicated by the PA_R control. The four thresholdsmay be selected such that comparing the TX_Gain for each PA rangeagainst the corresponding threshold is equivalent to comparing thetransmitter output power level against the switch point. A comparator514 receives the threshold from multiplexer 512 and the TX_Gain at twoinputs, provides a logic high if the TX_Gain exceeds the threshold, andprovides a logic low otherwise.

A logic unit 516 receives the output of comparator 514, a TX_EN signal,an INT_EN signal, and a Polarity signal. The TX_EN signal is at logichigh when transmitter 220 is enabled and at logic low otherwise. Whentransmitter 220 is enabled, the circuit blocks within transmitter 220are powered up, and transmitter 220 is ready for transmission. TheINT_EN signal is at logic high to enable circuit 500 and at logic lowotherwise. The Polarity signal indicates whether to generate aninterrupt if the TX_Gain is above the threshold (e.g., if SPS receiver260 is currently in the LP mode) or below the threshold (e.g., if SPSreceiver 260 is currently in the HL mode). Unit 516 generates a CTR_Ctrlsignal based on the input signals and provides the CTR_Ctrl signal to anUP/ DN input of an up/down counter 520. The CTR_Ctrl signal may be setequal to the output of comparator 514 (after any inversion by thePolarity signal) when the TX_EN signal is at logic high. The TX_ENsignal may be used to generate an interrupt if transmitter 220 is turnedoff and SPS receiver 260 is in the HL mode, so that an HL-to-LPtransition can take place.

An enable unit 518 receives the TX_EN signal, a TX_ON signal, and aCTR_EN signal and provides an output signal to an enable (EN) input ofcounter 520. The TX_ON signal is at logic high when transmitter 220 isactively transmitting and at logic low otherwise. The CTR_EN signal isat logic high to enable counter 520 and at logic low otherwise. Unit 518enables counter 520 when the CTR_EN signal is at logic high. Unit 518disables counter 520 when the TX_ON signal is at logic low and the TX_ENsignal is at logic high, so that counter 520 is not updated whentransmitter 220 is momentarily inactive, e.g., during punctured periodsor transmission gaps.

Counter 520 increments up or down based on the CTR_Ctrl signal from unit516 and when enabled by the output of unit 518. A comparator 522receives the output of counter 520 and a counter threshold CTR_TH at twoinputs and provides an interrupt SPS_INT if the counter output exceedsthe counter threshold.

FIG. 5 shows one design of an interrupt generation circuit. Otherdesigns may also be used to generate triggers for transitioning betweenthe HL and LP modes.

Transitions between the LP and HL modes may introduce jumps ordiscontinuities in gain, phase, and/or group delay of the SPS basebandsignal from driver 276 in SPS receiver 260. The gain jump may be handledby an automatic gain control (AGC) loop maintained for SPS. The phasejump may be characterized a priori and corrected with a digital rotatorwithin data processor 210 in order to compensate for phasediscontinuities. The group delay jump may be accounted for by aprogrammable delay unit within data processor. Performance degradationdue to jumps in gain, phase, and/or group delay may be reduced bylimiting the rate of transitions between the LP and HL modes.

Referring back to FIG. 2, the bias currents of various circuit blockswithin SPS receiver 260 may be varied based on the mode of the SPSreceiver. Each circuit block with variable bias current may beimplemented with various designs. Example designs for LNA 264, mixer266, and LO generator 286 are described below.

FIG. 6 shows a schematic diagram of a design of LNA 264 within SPSreceiver 260 in FIG. 2. In this design, LNA 264 is implemented with acascode common source with inductive degeneration topology. Thistopology may provide gain to mitigate noise of subsequent stages and mayalso introduce little additional noise, even with the circuitry used todynamically adjust the linearity of the LNA.

Within LNA 264, N-channel field effect transistors (N-FETs) 614 and 616are coupled in a cascode configuration. N-FET 614 has its gate receivingan SPS_In signal, its source coupled to one end of an inductor 612, andits drain coupled to the source of N-FET 616. The other end of inductor612 is coupled to circuit ground. N-FET 616 has its gate receiving a Vavoltage and its drain providing an SPS_Out signal. An inductor 618 and acapacitor 620 are coupled in parallel and between the drain of N-FET 616and a supply voltage, Vdd. Resistors 622 and 624 form a voltage dividernetwork, are coupled between the supply voltage and circuit ground, andprovide the Va voltage. A capacitor 626 is coupled between the gate ofN-FET 616 and circuit ground.

An N-FET 644 has its source coupled to one end of a resistor 642, itsgate coupled to an output of an operational amplifier (out amp) 640, andits drain coupled to one end of a switch 650. The other end of resistor642 is coupled to circuit ground. Switch 650 couples a bias currentsource 652 to the drain of N-FET 644 in the LP mode and couples a biascurrent source 654 to the drain of N-FET 644 in the HL mode. Biascurrent source 652 provides a bias current of Ib_low for the LP mode,and bias current source 652 provides a bias current of Ib_high for theHL mode.

An N-FET 646 has its gate receiving the Va voltage, its source coupledto one end of a current source 648, and its drain coupled to the supplyvoltage. The other end of current source 648 is coupled to circuitground. Op amp 640 has its non-inverting input coupled to the drain ofN-FET 644 and its inverting input coupled to the source of N-FET 646. Opamp 640 provides a bias voltage, Vbias, for N-FETs 614 and 644.Resistors 632 and 636 are coupled in series and between the gates ofN-FETs 644 and 614. A capacitor 634 is coupled between resistors 632 and636 and circuit ground.

Inductor 612 provides source degeneration for N-FET 614. Inductor 618and capacitor 620 form a tuned load that may be tuned to a desiredfrequency band, which is 1.57542 GHz for GPS. Resistor 632 and capacitor634 form a lowpass filter for the Vbias voltage from op amp 640.Resistor 636 provides isolation between the SPS_In signal and the Vbiasvoltage.

N-FET 644 forms a current minor for N-FET 614, with the bias current ofN-FET 614 minoring the bias current of N-FET 644. Resistor 642 modelsthe resistive loss of inductor 612 and allows for better matching of thegate-to-source voltages, V_(gs), for N-FETs 614 and 644. N-FET 646minors N-FET 616, with the source voltage of N-FET 646 closely matchingthe source voltage of N-FET 616, which is also the drain voltage ofN-FET 614. N-FET 646 thus provides access to the drain of N-FET 614,which is a sensitive node. Op amp 640 varies the Vbias voltage appliedto the gates of N-FETs 614 and 644 such that the gate-to-drain voltage,V_(gd), of N-FET 614 closely matches the V_(gd) of N-FET 644. Op amp 640thus ensures that the operating point of N-FET 614 closely matches theoperating point of N-FET 644. This feedback loop with op amp 640 allowsfor accurate control of the bias current of N-FET 614 using only a smallamount of bias current for N-FET 644. For example, if the desired biascurrent for N-FET 614 is Ibias, then N-FET 644 may be biased withIbias/X, where X may be a factor of 10 or more.

The cascode configuration in FIG. 6 may provide certain advantages suchas better isolation from the LNA input to the LNA output, higher LNAgain, higher output impedance, etc. The feedback loop with op amp 640may provide certain advantages such as better matching of the operatingpoints (e.g., V_(gd)) of N-FETs 614 and 644, which may allow for use ofa larger current ratio between N-FETs 614 and 644.

FIG. 7 shows a schematic diagram of a design of mixer 266 within SPSreceiver 260 in FIG. 2. In this design, mixer 266 includes a mixing core720 and a current buffer 730. Mixer 266 is implemented with a passivemixer with current buffer topology, which may improve noise performanceand provide bias current programmability based on linearityrequirements.

A transformer 710 couples the SPS_Out signal from LNA 264 to the inputof mixer 266. Transformer 710 is composed of primary inductor 618magnetically coupled to a secondary inductor 712. Inductor 618 is partof LNA 264 in FIG. 6. The differential voltage across inductor 712 isthe mixer input signal. Transformer 710 performs single-ended todifferential conversion and may further provide signal current gaindepending on the ratio of the number of turns in secondary inductor 712to the number of turns in primary inductor 618.

Within mixing core 720, a capacitor 722 a is coupled between one end ofinductor 712 and the drains of N-FETs 726 a and 726 b. A capacitor 724 ais coupled between the drains of N-FETs 726 a and 726 b and circuitground. Similarly, a capacitor 722 b is coupled between the other end ofinductor 712 and the drains of N-FETs 726 c and 726 d. A capacitor 724 bis coupled between the drains of N-FETs 726 c and 726 d and circuitground. The sources of N-FETs 726 a and 726 c are coupled together andto node A of mixer 266. The sources of N-FETs 726 b and 726 d arecoupled together and to node B of mixer 266. The gates of N-FETs 726 aand 726 d receive an inverting LO signal, LO−. The gates of N-FETs 726 band 726 c receive a non-inverting LO signal, LO+.

Within current buffer 730, a resistor 732 a is coupled between node Aand circuit ground. An N-FET 734 a has its source coupled to node A, itsgates receiving a Vb voltage, and its drain coupled to one end of acapacitor 742 a. A switch 736 a couples a bias current source 738 a tothe drain of N-FET 734 a in the LP mode and couples a bias currentsource 740 a to the drain of N-FET 734 a in the HL mode. Similarly, aresistor 732 b is coupled between node B and circuit ground. An N-FET734 b has its source coupled to node B, its gates receiving the Vbvoltage, and its drain coupled to one end of a capacitor 742 b. A switch736 b couples a bias current source 738 b to the drain of N-FET 734 b inthe LP mode and couples a bias current source 740 b to the drain ofN-FET 734 b in the HL mode. Bias current sources 738 a and 738 b providea bias current of Ib_lo for the LP mode, and bias current sources 740 aand 740 b provide a bias current of Ib_hi for the HL mode. The otherends of capacitors 742 a and 742 b provide a differential IF signal toamplifier 268.

Mixing core 720 implements a passive mixer that consumes no DC power, asshown by no DC paths for the drains of N-FETs 726 a through 726 d. Apassive mixer may provide better linearity and may generate less noisethan an active mixer. Capacitors 722 a and 722 b are AC couplingcapacitors. Capacitors 724 a and 724 b are used to model the parasiticcapacitance of switching devices N-FET 726 a through 726 d. N-FETs 726 athrough 726 d mix the RF signal from transformer 710 with thedifferential LO signal and provide the differential IF signal.

Current buffer 730 is implemented with a common gate current buffertopology. Resistors 732 a and 732 b, selected bias current sources 738or 740, and voltage Vb at the gates of N-FETs 734 a and 734 b set thebiasing point for current buffer 730. N-FETs 734 a and 734 b buffer thedifferential current signal from mixing core 720 and isolate amplifier268 from the mixing core. Capacitors 742 a and 742 b are AC couplingcapacitors.

FIG. 8 shows a schematic diagram of a design of LO generator 286 for SPSreceiver 260 in FIG. 2. Within LO generator 286, a switch 812 receives avoltage controlled oscillator (VCO) signal from PLL 282, passes the VCOsignal to a high linearity divider/buffer 814 when the HL mode isselected, and passes the VCO signal to a low power divider/buffer 816when the LP mode is selected. Either divider/buffer 814 or 816 may bepowered on at any given moment depending on the mode of SPS receiver260. A switch 818 provides the output of divider/buffer 814 as the LOsignal for mixer 266 when the HL mode is selected and provides theoutput of divider/buffer 816 when the LP mode is selected.

FIGS. 6, 7 and 8 show example designs of LNA 264, mixer 266, and LOgenerator 286 for two modes. Other designs may also be used for thesecircuit blocks. Furthermore, more than two modes may be supported byeach circuit block.

FIG. 9 shows a design of a process 900 for operating an SPS receiver,e.g., a GPS receiver. Process 900 may be performed by processor 210,controller 216, processor 290, unit 278, etc., in FIG. 2. An outputpower level of a transmitter that is co-located with the SPS receivermay be determined (block 912). The transmitter may be a CDMA transmitteror some other type of transmitter. The transmitter and the SPS receivermay be co-located if they are implemented on the same integrated circuit(IC), the same circuit board, the same wireless device, etc. Thetransmitter output power level may be determined based on the range of aPA within the transmitter and a gain of the transmitter, as describedabove, or in some other manner.

Bias current of the SPS receiver may be adjusted based on the outputpower level of the transmitter (block 914). The SPS receiver maycomprise at least one circuit block with adjustable bias current, e.g.,a LNA, a mixer, an LO generator, etc. The bias current of each circuitblock may be adjusted based on the transmitter output power level.

A state machine comprising a plurality of states may be maintained. Forexample, the state machine may comprise the states shown in FIG. 4. Eachstate may be associated with a particular mode for the SPS receiver anda particular mode for the transmitter. The bias current of the SPSreceiver may be selected based on the current state in the statemachine.

The SPS receiver may be operated in one of a plurality of modes, whichmay be associated with different bias current settings for the SPSreceiver. One of the modes may be selected based on the transmitteroutput power level and at least one switch point. The bias current ofthe SPS receiver may be set based on the selected mode.

FIG. 10 shows a design of block 914. In this design, the transmitteroutput power level may be compared against a switch point (block 1012).A first mode (e.g., a low power mode) may be selected for the SPSreceiver if the transmitter output power level is below the switch point(block 1014). A second mode (e.g., a high linearity mode) may beselected for the SPS receiver if the transmitter output power level isabove the switch point (block 1016). The second mode is associated withmore bias current for the SPS receiver than the first mode.

An interrupt may be received when the transmitter output power levelexceeds the switch point. The second mode for the SPS receiver may beselected in response to receiving the interrupt. While the SPS receiveris in the second mode, polling may be performed to determine whether thetransmitter output power level is below the switch point. The first modemay be selected when the polling indicates that the transmitter outputpower level is below the switch point. Whether the transmitter outputpower is above or below the switch point may also be determined in othermanners. Time hysteresis and/or signal hysteresis may be used fortransitions between the first and second modes.

The techniques described herein may be implemented by various means. Forexample, these techniques may be implemented in hardware, firmware,software, or a combination thereof. For a hardware implementation, theprocessing units used to determine the operating mode of an SPS receiverand to adjust bias current of the SPS receiver may be implemented withinone or more ASICs, DSPs, digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors,electronic devices, other electronic units designed to perform thefunctions described herein, a computer, or a combination thereof.

For a firmware and/or software implementation, the techniques may beimplemented with modules (e.g., procedures, functions, etc.) thatperform the functions described herein. The firmware and/or softwareinstructions may be stored in a memory (e.g., memory 292 in FIG. 2) andexecuted by a processor (e.g., processor 290). The memory may beimplemented within the processor or external to the processor. Thefirmware and/or software instructions may also be stored in otherprocessor-readable medium such as random access memory (RAM), read-onlymemory (ROM), non-volatile random access memory (NVRAM), programmableread-only memory (PROM), electrically erasable PROM (EEPROM), FLASHmemory, compact disc (CD), magnetic or optical data storage device, etc.

The circuit blocks described herein (e.g., LNA 264 in FIG. 6, mixer 266in FIG. 7, LO generator 286 in FIG. 8, etc.) may be implemented withvarious types of transistors such as N-FETs, P-FETs, metal oxidesemiconductor FETs (MOSFETs), bipolar junction transistors (BJTs),gallium arsenide (GaAs) FETs, etc. These circuit blocks may also befabricated in various IC processes and in various types of IC such as RFICs (RFICs), mixed-signal ICs, etc.

An apparatus implementing the techniques or circuit blocks describedherein may be a stand-alone unit or may be part of a device. The devicemay be (i) a stand-alone IC, (ii) a set of one or more ICs that mayinclude memory ICs for storing data and/or instructions, (iii) an ASICsuch as an MSM, (iv) a module that may be embedded within other devices,(v) a cellular phone, wireless device, handset, or mobile unit, (vi)etc.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method of selecting a mode for an SPS receiver,the method comprising: selecting either a first mode or a second modefor the SPS receiver based on a comparison between an output power of acommunications transceiver and a mode switch point wherein the modeswitch point is a power value; wherein the first mode corresponds to afirst bias current value of the SPS receiver, the second modecorresponds to a second bias current value of the SPS receiver, and thefirst bias current value is different from the second bias currentvalue.
 2. The method of claim 1 further comprising determining the modeswitch point based on a communications network environment of a mobiledevice.
 3. The method of claim 2 further comprising determining the modeswitch point based on a probability density function of the outputpower.
 4. The method of claim 1 further comprising performing polling todetermine if the output power exceeds the mode switch point.
 5. Themethod of claim 1 wherein the mode switch point is a first mode switchpoint, and further comprising: transitioning from selecting the firstmode to selecting the second mode based on the output power rising abovethe first mode switch point; and transitioning from selecting the secondmode to selecting the first mode based on the output power droppingbelow a second mode switch point wherein the second mode switch point islower than the first mode switch point.
 6. A mobile device comprising: acommunications transceiver; a satellite positioning system (SPS)receiver; and a processor configured to select either a first mode or asecond mode for the SPS receiver based on a comparison between an outputpower of the communications transceiver and a mode switch point whereinthe mode switch point is a power value; wherein the first modecorresponds to a first bias current value of the SPS receiver, thesecond mode corresponds to a second bias current value of the SPSreceiver, and the first bias current value is different from the secondbias current value.
 7. The mobile device of claim 6 wherein theprocessor is further configured to determine the mode switch point basedon a communications network environment of the mobile device.
 8. Themobile device of claim 7 wherein the processor is further configured todetermine the mode switch point based on a probability density functionof the output power.
 9. The mobile device of claim 6 wherein theprocessor is further configured to perform polling to determine if theoutput power exceeds the mode switch point.
 10. The mobile device ofclaim 6 wherein the mode switch point is a first mode switch point, andthe processor is further configured to: transition from selecting thefirst mode to selecting the second mode based on the output power risingabove the first mode switch point; and transition from selecting thesecond mode to selecting the first mode based on the output powerdropping below a second mode switch point wherein the second mode switchpoint is lower than the first mode switch point.
 11. An apparatus forselecting a mode for an SPS receiver, the apparatus comprising: meansfor selecting either a first mode or a second mode for the SPS receiverbased on a comparison between an output power of a communicationstransceiver and a mode switch point wherein the mode switch point is apower value; wherein the first mode corresponds to a first bias currentvalue of the SPS receiver, the second mode corresponds to a second biascurrent value of the SPS receiver, and the first bias current value isdifferent from the second bias current value.
 12. The apparatus of claim11 further comprising means for determining the mode switch point basedon a communications network environment of a mobile device.
 13. Theapparatus of claim 12 further comprising means for determining the modeswitch point based on a probability density function of the outputpower.
 14. The apparatus of claim 11 further comprising means forperforming polling to determine if the output power exceeds the modeswitch point.
 15. The apparatus of claim 11 wherein the mode switchpoint is a first mode switch point, and further comprising: means fortransitioning from selecting the first mode to selecting the second modebased on the output power rising above the first mode switch point; andmeans for transitioning from selecting the second mode to selecting thefirst mode based on the output power dropping below a second mode switchpoint wherein the second mode switch point is lower than the first modeswitch point.
 16. An article comprising at least one storage mediumhaving stored thereon instructions executable by one or more processorsto: select either a first mode or a second mode for an SPS receiverbased on a comparison between an output power of a communicationstransceiver and a mode switch point wherein the mode switch point is apower value; wherein the first mode corresponds to a first bias currentvalue of the SPS receiver, the second mode corresponds to a second biascurrent value of the SPS receiver, and the first bias current value isdifferent from the second bias current value.
 17. The article of claim16 wherein the instructions executable by the one or more processorsfurther comprise instructions to determine the mode switch point basedon a communications network environment of a mobile device.
 18. Thearticle of claim 17 wherein the instructions executable by the one ormore processors further comprise instructions to determine the modeswitch point based on a probability density function of the outputpower.
 19. The article of claim 16 wherein the instructions executableby the one or more processors further comprise instructions to performpolling to determine if the output power exceeds the mode switch point.20. The article of claim 16 wherein the mode switch point is a firstmode switch point, and the instructions executable by the one or moreprocessors further comprise instructions to: transition from selectingthe first mode to selecting the second mode based on the output powerrising above the first mode switch point; and transition from selectingthe second mode to selecting the first mode based on the output powerdropping below a second mode switch point wherein the second mode switchpoint is lower than the first mode switch point.